U.S. patent application number 11/237667 was filed with the patent office on 2006-07-13 for display filter.
This patent application is currently assigned to FUJITSU HITACHI PLASMA DISPLAY LIMITED. Invention is credited to Takatoshi Hirota, Nobuyuki Hori, Yoshimi Kawanami.
Application Number | 20060152127 11/237667 |
Document ID | / |
Family ID | 35478458 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060152127 |
Kind Code |
A1 |
Kawanami; Yoshimi ; et
al. |
July 13, 2006 |
Display filter
Abstract
A display filter is provided that can realize price reduction
without lowering electromagnetic wave shielding ability and near
infrared rays shielding ability. A conductive mesh is used for
shielding electromagnetic waves. A multilayered film and a coloring
layer are used for shielding near infrared rays. The multilayered
film reflects near infrared rays selectively and the coloring layer
absorbs near infrared rays selectively. The use of the multilayered
film significantly reduces near infrared rays absorption ability
that is required for the coloring layer compared to the case where
no multilayered film is used.
Inventors: |
Kawanami; Yoshimi;
(Miyazaki-shi, JP) ; Hirota; Takatoshi;
(Kawasaki-shi, JP) ; Hori; Nobuyuki;
(Miyazaki-shi, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
FUJITSU HITACHI PLASMA DISPLAY
LIMITED
Kawasaki
JP
|
Family ID: |
35478458 |
Appl. No.: |
11/237667 |
Filed: |
September 29, 2005 |
Current U.S.
Class: |
313/112 |
Current CPC
Class: |
H01J 11/10 20130101;
G02B 5/223 20130101; H01J 11/44 20130101; G02B 5/208 20130101; H05K
9/0096 20130101; G02B 5/281 20130101; H01J 2211/446 20130101; G02B
5/204 20130101 |
Class at
Publication: |
313/112 |
International
Class: |
H01J 5/16 20060101
H01J005/16 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2004 |
JP |
2004-284880 |
Claims
1. A display filter comprising: a conductive mesh for shielding an
electromagnetic wave; a multilayered film for reflecting near
infrared rays selectively; and a coloring layer for absorbing the
near infrared rays selectively, wherein the conductive mesh, the
multilayered film and the coloring layer are laminated
together.
2. The display filter according to claim 1, wherein transmittance
of near infrared rays having a wavelength of 830 nm and of near
infrared rays having a wavelength of 880 nm is equal to or less
than 5%.
3. The display filter according to claim 1, wherein the
multilayered film is a layered film of plural dielectric layers
each of which has a different refractive index for the near
infrared rays.
4. The display filter according to claim 1, wherein the
multilayered film is a layered film of a dielectric and metal.
5. The display filter according to claim 1, wherein the
multilayered film is placed on a rear side of the coloring
layer.
6. A display panel device, comprising: a plasma display panel; and
a translucent front sheet that is glued on a front face of the
plasma display panel, wherein the front sheet includes a conductive
mesh for shielding an electromagnetic wave, a coloring layer for
absorbing near infrared rays selectively, and a multilayered film
for attenuating the near infrared rays selectively.
7. The display panel device according to claim 6, further
comprising an adhesive layer for bonding the front sheet and the
plasma display panel together.
8. The display panel device according to claim 7, wherein the
adhesive layer has a thickness equal to or more than 100 microns.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to display filters for
shielding electromagnetic waves and near infrared rays both of
which are emitted by displays. The present invention is suitable
for plasma display panels that are one type of flat panel
displays.
[0003] 2. Description of the Related Art
[0004] Plasma display panels each incorporate an electromagnetic
wave shield and an optical filter therein as EMI countermeasures.
The electromagnetic wave shield serves to shield electromagnetic
waves that are generated by applying drive voltage. The optical
filter (hereinafter referred to as an NIR filter) serves to shield
near infrared rays that are emitted by a discharge gas. Japanese
Patent No. 3145309, for example, discloses a structure in which an
electromagnetic wave shield made up of a transparent conductive
film and an NIR filter made up of a multilayered film are formed on
a front face of a plasma display panel.
[0005] The use of metal mesh as electromagnetic wave shields has
recently become common. Since the metal mesh is superior to
transparent conductive films in electric conductivity, it is
suitable for providing sufficient shielding function in large
screens. The metal mesh, however, is incapable of shielding near
infrared rays sufficiently, because it has no selectivity in
translucent wavelength. Japanese Patent No. 3480898 describes a
specific example of the metal mesh.
[0006] NIR filters for shielding near infrared rays sufficiently in
a selective manner can be realized by coloring matters having
desired light absorption properties. When the NIR filters are used
in combination with coloring matters that absorb visible lights, a
color filter function can be given to the NIR filters. Japanese
Unexamined Patent Publication No. 2002-123180 describes a specific
example of coloring matters suitable for the NIR filters.
[0007] A content of a coloring matter determines near infrared rays
shielding ability of an NIR filter including a coloring film. It is
necessary to increase the content of the coloring matter in order
to improve performance. A problem arises, however, in which the
improvement in performance of an NIR filter increases a production
cost significantly, since a coloring matter that absorbs near
infrared rays selectively is expensive.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to solve the problem
pointed out above, and therefore, an object of the present
invention is to realize a low cost without lowering electromagnetic
wave shielding ability and near infrared rays shielding ability.
Another object of the present invention is to enhance the near
infrared rays shielding ability without lowering the
electromagnetic wave shielding ability and raising price.
[0009] According to the present invention, conductive mesh is used
for shielding electromagnetic waves, and a multilayered film and a
coloring layer are used in combination with each other for
shielding near infrared rays. The mulilayered film attenuates near
infrared rays selectively and the coloring layer absorbs near
infrared rays selectively. The use of the multilayered film
significantly lowers near infrared rays absorption ability required
for the coloring layer in comparison to the case where no
multilayered film is used. This is because near infrared rays
transmittance of a filter is a product of transmittance in the
coloring layer and transmittance in the multilayered film, not
simply because the multilayered film compensates for a lowered part
of the near infrared rays absorption ability in the coloring layer.
Using the multilayered film can reduce coloring matter usage.
[0010] According to the present invention, it is possible to
realize price reduction of a filter without lowering
electromagnetic wave shielding ability and near infrared rays
shielding ability.
[0011] These and other characteristics and objects of the present
invention will become more apparent by the following descriptions
of preferred embodiments with reference to drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows an appearance of a display device according to
the present invention.
[0013] FIG. 2 shows a structure of a display panel device.
[0014] FIG. 3 shows an example of a structure of the display
device.
[0015] FIG. 4 shows a layer structure of a front sheet.
[0016] FIGS. 5A-5C show a general outline of filter characteristics
according to the present invention.
[0017] FIG. 6 is a graph showing a relationship between a coloring
matter concentration and transmittance.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] FIG. 1 shows an appearance of a display device according to
the present invention. A display device 100 is a flat type display
having a 32-inch diagonal screen 50. Dimensions of the screen 50
are 0.72 meters in the horizontal direction and 0.40 meters in the
vertical direction. A facing cover 101 that defines a plane size of
the display device 100 has an opening that is larger than the
screen 50, so that a front face of a display panel device 1 is
exposed partly.
[0019] FIG. 2 shows a structure of the display panel device. The
display panel device 1 includes a plasma display panel 2 that is a
device that constitutes a screen and a front sheet 3 that is glued
directly on the front face of the plasma display panel 2 to be a
display face. The front sheet 3 is a sheet-like structure including
a display filter according to the present invention. The plasma
display panel 2 is a self-luminous type device that emits light by
gas discharge, which includes a front face plate 10 and a rear face
plate 20. Each of the front face plate 10 and the rear face plate
20 is a structural element having a base of a glass plate having a
thickness of approximately 3 mm.
[0020] The plasma display panel 2 is filled with a Penning gas that
is a mixture of neon and xenon (equal to or more than 2%) as a
discharge gas. This Penning gas emits near infrared rays having a
wavelength of 830 nm and a wavelength of 880 nm at discharge.
[0021] FIG. 3 is a cross-sectional cut along a-a line in FIG. 1 and
shows a structure of the display device. The display device 100
includes a display panel device 1 arranged in a conductive housing
102 to which the facing cover 101 is attached. The display panel
device 1 is attached to a chassis 105 made of aluminum via a
thermal conducting adhesive tape 104, and the chassis 105 is fixed
to the conductive housing 102 via spacers 106 and 107. A driving
circuit 90 is arranged on the rear side of the chassis 105. A power
source, a video signal processing circuit and an audio circuit are
omitted in FIG. 3.
[0022] The front sheet 3 is a flexible layered film including a
front portion 3A having a thickness of 0.3 mm whose base is a resin
film and a rear portion 3B having a thickness of approximately 0.5
mm made of a resin layer that are put on each other, which will be
described later. In particular, the thin front portion 3A that is a
functional film having a multilayered structure has a good
flexibility. The plane size of the front sheet 3, more specifically
the plane size of the front portion 3A is larger than the plane
size of the plasma display panel 2, so that the peripheral portion
of the front portion 3A is positioned outside the plasma display
panel 2. The plane size of the rear portion 3B is smaller than that
of the front portion 3A and larger than that of the screen.
[0023] The conductive housing 102 is a metal plate formed in a
boxed shape having a rectangular rear face, four side faces and a
looped front face. The conductive housing 102 is also a conductive
member that covers the side faces and the rear face of the plasma
display panel 2 with being spaced apart therefrom. Inner rim of the
front face of the conductive housing 102 is placed outside the
plasma display panel 2 as viewed from the front.
[0024] In the display device 100, the front sheet 3 extends along
the plasma display panel 2 substantially in flat, and only the end
portion thereof contacts the front face of the conductive housing
102. A looped pressure member 103 is disposed in front of the front
sheet 3, which is sandwiched between the pressure member 103 and
the front face of the conductive housing 102 so that the end
portion of the front sheet 3 is fixed to the conductive housing
102. Here, the front portion 3A includes an electromagnetic wave
shielding layer 320 having a function of preventing halation. The
electromagnetic wave shielding layer 320 is a rear side layer of
the front portion 3A. A plane size of the front portion 3A is the
same as that of the front sheet 3 and is larger than that of the
rear portion 3B. Accordingly, when the front sheet 3 is fixed to
the conductive housing 102, the electromagnetic wave shielding
layer 320 is connected to the conductive housing 102 electrically.
The connection position thereof is away from the plasma display
panel 2.
[0025] FIG. 4 shows a layer structure of the front sheet. The front
sheet 3 is a layered film having a thickness of approximately 0.8
mm including an optical film layer 310 having a thickness of 0.2
mm, an electromagnetic wave shielding layer 320 having a thickness
of 0.1 mm and the rear portion 3B that is an adhesive layer having
an impact absorbing function with a thickness of approximately 0.5
mm. The optical film layer 310 and the electromagnetic wave
shielding layer 320 constitute the front portion 3A, and the plane
sizes of them are the same. A visible light transmittance of the
entire front sheet 3 is approximately 40% after spectral luminous
efficiency correction. A weight of the front sheet 3 is
approximately 500 grams, so the front sheet 3 is much lighter than
a conventional filter plate (approximately 2.5 kilograms) for
32-inch screen.
[0026] The optical film layer 310 includes a film 311 made of PET
(polyethylene terephthalate), an anti-reflection film 312 that is
coated on the front side of the film 311, a coloring layer 313 that
is formed on the rear side of the film 311, a film 315 and a
multilayered film 316, which is unique to the present invention,
formed on the rear side of the film 315.
[0027] The anti-reflection film 312 prevents reflection of external
light. The function of the anti-reflection film 312, however, may
be changed from AR (anti reflection) to AG (anti glare). The
anti-reflection film 312 includes a hard coat for increasing
scratch resistance of the surface of the sheet up to pencil
hardness 4H.
[0028] The coloring layer 313 adjusts visible light transmittance
of red (R), green (G) and blue (B) for a color display and cuts off
near infrared rays. The coloring layer 313 contains in a resin an
infrared absorption coloring matter for absorbing light having a
wavelength within the range between approximately 800 and 1000 nm,
a neon light absorption coloring matter for absorbing light having
a wavelength of approximately 580 nm and a coloring matter for
adjusting visible light transmittance. An external light reflection
factor of the optical film layer 310 is 3% after the spectral
luminous efficiency correction, and the visible light transmittance
is 55% after the spectral luminous efficiency correction. In
addition, near infrared rays transmittance is 10% as an average in
an absorption wavelength range.
[0029] The multilayered film 316 cuts off near infrared rays. The
multilayered film 316 is a layered film that is formed by
sputtering a dielectric material and metal (silver, for example)
alternately or others. The multilayerd film 316 reflects near
infrared rays having a wavelength within the range between
approximately 800 and 1000 nm by multiple interference. Near
infrared rays transmittance in the multilayered film 316 is 40% as
an average in the wavelength range between approximately 800 and
1000 nm.
[0030] Variations of the structure of the multilayered film 316
include a laminate of a dielectric material having a low refractive
index such as MgF.sub.2, SiO.sub.2, or the like and a dielectric
material having a high refractive index such as ZrO.sub.2,
Ta.sub.2O.sub.5, TiO.sub.2 or the like. The laminate of metal and a
dielectric material is advantageous in that the number of layers is
reduced, since it can increase the dielectric constant difference.
In particular, silver is a suitable material since it has a
function of absorbing near infrared rays.
[0031] The electromagnetic wave shielding layer 320 includes a film
321 made of PET and a conductive layer 322 having a thickness of 10
microns that is a copper foil with a mesh portion. The visible
light transmittance of an area of the conductive layer 322 that
overlaps the screen is 80%. As the front surface of the conductive
layer 322 is black, the electromagnetic wave shielding layer 320
looks substantially coal-black when it is viewed through the
optical film layer 310.
[0032] The films 311 and 315 of the optical film layer 310 and the
film 321 of the electromagnetic wave shielding layer 320 have a
function of preventing a glass plate of the plasma display panel 2
from scattering when the glass plate is broken in an abnormal
situation. In order to realize this function, it is preferable that
a total thickness of the films 311 and 315 and the film 321 is 50
microns or more. In this example, a total sum of the thickness of
the PET is equal to or more than 150 microns.
[0033] The adhesive layer as the rear portion 3B is made of a soft
resin of an acrylic system, and a visible light transmittance
thereof is 90%. The adhesive layer (3B) is formed by applying the
resin. When the resin is applied, it enters spaces of the mesh of
the conductive layer 322, so that the conductive layer 322 is
flattened. Thus, scattering of light due to unevenness of the
conductive layer 322 can be prevented.
[0034] In this example, the adhesive layer (3B) has an impact
absorbing function. The adhesive layer (3B) has relatively strong
adhesiveness to the electromagnetic wave shielding layer 320 made
of PET and copper. On the contrary, the adhesive layer (3B) has
loose adhesiveness to the glass surface that is the front face of
the plasma display panel 2. The adhesion force thereof is
approximately 2N/25 mm. When the front sheet 3 is peeled, the front
portion 3A is not separated from the rear portion 3B so that the
front sheet 3 is separated from the plasma display panel 2
normally. "Normally" means that an even peeled surface without a
visible remaining matter can be obtained.
[0035] The sufficient thickness of the rear portion 3B constituted
by the adhesive layer 351 contributes to improvement in
productivity of plasma display panel modules. The plasma display
panel module in the present embodiment is the plasma display panel
2 where a driving circuit is incorporated and the front sheet 3 is
glued and means a half-finished product that is accommodated in the
conductive housing 102 in the display device 100 shown in FIG.
3.
[0036] In manufacture of plasma display panel modules, foreign
matters may be mixed in a bonding interface when a front sheet is
glued on the plasma display panel 2. If the rear portion 3B
constituted by the adhesive layer has a thickness similar to the
size of the foreign matter, air bubbles appear around the foreign
matter. Accordingly, the front sheet needs to be glued in a clean
room in order to avoid the mixing of foreign matters. In such a
case, however, the front sheet is glued on the plasma display panel
prior to an aging test and a lighting test of the plasma display
panel. In the event that the plasma display panel is determined to
be defective after the lighting test, the front sheet is waste in
addition to the plasma display panel. Even if the front sheet has a
peelable and reproducible structure, a process for peeling the
front sheet is added.
[0037] In contrast, even when a foreign matter having a size of
approximately a few tens of microns is mixed, no air bubbles
appear, provided that the rear portion (adhesive layer) 3B has a
thickness equal to or more than 100 microns (preferably, 200
microns through 500 microns=0.2 mm thorough 0.5 mm). This is
because the foreign matter buries in the soft rear portion 3B.
Accordingly, a chassis for heat dissipation and a driving circuit
are incorporated in the plasma display panel 2 and a lighting test
is performed. Then, the front sheet 3 is glued on the plasma
display panel 2 that passed the lighting test. This can eliminate
time loss and resource loss such as a front sheet that is discarded
or peeled.
[0038] In addition, a material having good wettability to glass
that is a base material of the front face plate of the plasma
display panel is used as a material for the adhesive layer. This
can prevent the appearance of air bubbles due to foreign matters
even under decompression environment in uplands (3000 meters above
sea level, for example).
[0039] FIGS. 5A-5C show a general outline of filter characteristics
according to the present invention.
[0040] FIG. 5A shows characteristics of the coloring layer 313. The
average transmittance of light having a predetermined wavelength
range between 800 and 1000 nm is 10% in the coloring layer 313. The
average transmittance does not satisfy a value of 5% that is a
specification of near infrared rays absorption ability. In
comparison to conventional filters that satisfy specifications, a
content of the coloring matter is reduced in the coloring layer
313, which reduces the near infrared rays absorption ability by
design. The purpose of the reduction is to make the coloring layer
313 inexpensive.
[0041] FIG. 5B shows characteristics of the multilayered film 316.
The transmittance of light having a wavelength range between 800
and 1000 nm is equal to or less than 50% in the multilayered film
316.
[0042] FIG. 5C shows characteristics of a filter according to the
present invention, i.e., a layered film of the coloring layer 313
and the multilayered film 316. The transmittance of light having a
noted wavelength in the filter is a product of the transmittance of
such light in the coloring layer 313 and the transmittance of such
light in the multilayered film 316. More specifically, even when
the transmittance in the coloring layer 313 is 10%, the
transmittance in the multilayered film 316 is equal to or less than
50%. Accordingly, the transmittance of light having a wavelength
range between 800 and 1000 nm in the filter is equal to or less
than 5%, so that specifications are satisfied.
[0043] FIG. 6 is a graph showing a relationship between a coloring
matter concentration and transmittance.
[0044] Suppose that an amount of the coloring matter is denoted by
M, transmittance T of light having a certain wavelength is defined
as the following equation. T=exp(-aM) where a is a coefficient
representing absorption ability.
[0045] When M is a small value, T can approximate 1-aM
(T.apprxeq.1-aM). The transmittance decreases linearly with
increasing a value of M. However, saturation is gradually reached
as a value of T approaches zero.
[0046] Suppose that M necessary for making the transmittance 10% is
1. The value of M needs to be 1.3 in order to make the
transmittance 5%. In other words, it is necessary to increase the
coloring matter by 30%. More specifically, when absorption ability
is reduced from the transmittance of 5% to the transmittance of
10%, reduction from 1.3 to 1, i.e., 23 percent reduction of the
coloring matter amount (cost reduction) is expected. In practice,
the relationship between the coloring matter concentration and the
transmittance is looser than theoretical values due to
ununiformness of coloring matter distribution, leading to a
substantial cost reduction effect.
[0047] In the present embodiment, the coloring layer 313 and the
multilayered film 316 are superimposed one over the other to
constitute the NIR filter. Accordingly, a filter having high
ability of shielding near infrared rays can be easily realized in
comparison to a case where the NIR filter is made up of only the
coloring layer or of only the multilayered film.
[0048] The performance of the multilayered film is enhanced with
increasing the number of layers. Increasing the number of layers,
however, raises a production cost. Accordingly, it is necessary to
design the coloring layer 313 and the multilayered film 316 so that
the cost reduction due to the reduction of the coloring matter
amount in the coloring layer 313 exceeds the cost increase due to
the use of the multilayered film 316.
[0049] An arrangement position of the multilayered film 316 is
closer to the plasma display panel 2 compared to the coloring layer
313. This arrangement substantially reduces reflection of red
components of external light from the multilayered film 316
compared to another arrangement where the multilayered film 316 is
placed ahead of the coloring matter 313. Accordingly, the former
arrangement is preferred to the latter arrangement in that
neutrality of appearance color of the front sheet 3 is
maintained.
[0050] In this embodiment described above, the structure is
exemplified in which a filter is provided in the front sheet 3 that
is directly glued on the front face plate of the plasma display
panel 2. In a structure where a protection plate is arranged in
front of the plasma display panel 2, the filter may be glued on the
protection plate.
[0051] The present invention contributes to provision of
inexpensive display filters for shielding electromagnetic waves and
near infrared rays both of which are emitted by displays.
[0052] While example embodiments of the present invention have been
shown and described, it will be understood that the present
invention is not limited thereto, and that various changes and
modifications may be made by those skilled in the art without
departing from the scope of the invention as set forth in the
appended claims and their equivalents.
* * * * *